This invention relates to high power gas transport lasers and more particularly to an improved starting element for such a laser.
In order to initiate electrical discharge between electrodes of a gas transport laser as described in U.S. Pat. No. 3,772,610, a separate electrode is mounted adjacent to the cathode and preionizes the gap between the cathode and anode of the laser. Such a starter element has performed satisfactorily for a laser having a single set or pair of electrodes, i.e., one cathode and one anode, but is not effective in a laser having two or more sets of electrodes connected in parallel across the high voltage DC power supply. Such a multi-electrode laser is described in copending application Ser. No. 773,826 of R. J. Pressley et al, now Pat. No. 4,114,114, assigned to the assignee of this invention. As the voltage is raised to initiate a two-cathode discharge, one cathode discharge invariably starts first due to unavoidable impedance differences between the two sets of electrodes, and because of the resultant voltage drop when the main discharge occurs, the second cathode discharge is unable to start.
In U.S. Pat. No. 4,114,114, preionization of the gaps between the two sets of laser electrodes is achieved by applying a pulse or series of pulses simultaneously to the anodes from a common power source through a transformer. This technique is effective to start the main electrical discharges between both sets of electrodes and thus reliably to start the laser. Implementation of this technique, however, requires that high voltage insulation be added to the anode pads to which the starting pulses are applied to prevent inter-pad arcing. Such anode design changes together with the need for transformer equipment have added to the complexity and cost of the laser.
This invention is directed to an improved solution of the laser starting problem.